I have a problem with my bike and that would be great if anyone could help me. When I try to turn the pedal backward,with hand, the rear derailleur doesn't turn with the chain. When biking, if I stop pedaling the engagement between the chain and rear derailleur is lost and according to the speed, I need to pedal several turns for having the chain engaged with the rear derailleur again to move forward.

If you turn slowly back and the chain doesn't run freely over the rear cogs then it sounds like your freewheel has packed up, which will probably mean replacing it.
I would visit your LBS for their opinion, but be careful when riding, if this is the cause, then if you stop pedaling while riding the chain can wrap up and jam the wheel.

(09-10-2010, 07:55 AM)alireza Wrote: [quote='Luna' pid='10760' dateline='1284069947']
I have the same problem.... did you get yours fixed?

No. I haven't found a solution yet.
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Hi, my dad found the problem... you just need to change the freewheel or cassette, depends on your bike. First just to make sure we have the same thing going on, have some one help you remove the wheel, if the freewheel or cassette is very loose than that is the problem... below are the links that helped me. It was less thank $20 to fix, the bike shop was charging $43.

(09-10-2010, 02:41 PM)trevgbb Wrote: If you turn slowly back and the chain doesn't run freely over the rear cogs then it sounds like your freewheel has packed up, which will probably mean replacing it.
I would visit your LBS for their opinion, but be careful when riding, if this is the cause, then if you stop pedaling while riding the chain can wrap up and jam the wheel.